1. Field of the Invention
The invention relates to a packing with a cross channel structure for a material exchange column with a high specific separation performance, to a column with a packing of this kind and to a method for the operation of a column of this kind.
2. Description of the Prior Art
Packings with cross channel structure have already been known for many years (see e.g. DE-A 26 01 890). They are assembled as a rule from a plurality of packing elements which are arranged one above the other, with each packing element being constructed of a large number of parallel layers. The layers make contact and form the cross channel structure with mutually open flow passages which are inclined with respect to the vertical (column axis). A material and/or heat exchange can be carried out with a column packing of this kind, namely between a ripple film on the packing surface and a gas flow which flows through the passages.
In a standard treatise on distillation (H. Z. Kister, xe2x80x9cDistillation Designxe2x80x9d, McGraw-Hill, Inc. 1992; pages 441-458) packings with cross channel structure for carrying out material separation processes are discussed. These packings are optimally utilizable when the specific separation performances which are required are not too high. The specific separation performance can be quantified through a parameter NTSM which specifies the number n of theoretical stages per meter (or in Kister the parameter HETP, xe2x80x9cheight equivalent of a theoretical platexe2x80x9d, which is measured in inches and is substantially the reciprocal value of the parameter NTSM). The specific separation performance is considered here to be high when NTSM is greater than 4.5 mxe2x88x921 (i.e. n greater than 4.5).
In known uses it has turned out in practice that a class of packings in which the angle of inclination of the passages is in each case equally large is optimally utilizable. In the named treatise 45xc2x0 is given as the value for this angle of inclination (see Kister, Table 8.1, in particular the class of packings xe2x80x9cMellapak(copyright)xe2x80x9d 125.Y, 250.Y, 350.Y and 500.Y). In the packing class of xe2x80x9cMellapak(copyright)xe2x80x9d (hereinafter, packings 125.Y, . . . ) this angle does not amount to 45xc2x0 but rather to 42.5xc2x0; this angle has proven to be more favorable.
The inventor was confronted with the problem of making packings available for separation columns for which the specific separation performance is high and which is advantageous in particular in methods for air decomposition. In this he recognized that it is recommendable to carry out further basic experiments with respect to the manner of action of the packings with cross channel structure in order thus to be able to propose criteria for more economical packings as a result of newly won results.
The object of the invention is to create a packing with cross channel structure which is distinguished by a high specific separation performance and which enables as economical a separation process as possible. This object is satisfied by packings such as a packing with cross channel structure for a material exchange column having a high specific separation performance. The packing is specifiable by a specific surface area, a, and an inclination angle of the passages, A. It belongs to a class of packings with a =acl and xcfx86=xcfx86cl in accordance with the following assertions:
for fluids which flow in the packing, equally large fluid flows are in each case provided for all packings;
a number n of theoretical separation stages per meter which can be empirically determined for the packing, namely the parameter NTSM, can be represented by a first function f1(a, xcfx86) of the variables a and xcfx86;
a flow resistance which results for a gas flow which flows through the packing can be characterized by a pressure loss per meter, xcex94p, as a second function f2(a, xcex94);
under the auxiliary condition n=const, xcex94p assumes a relative minimum for which the variables a and xcfx86xe2x80x94in dependence on the parameter nxe2x80x94assume the values am(n) and xcfx86m(n) respectively;
it is true that n greater than 4.5, acl less than am(n), xcfx86cl greater than xcfx86m(n) and xcfx86cl greater than 45xc2x0.
The invention will be illustrated with reference to two examples:
The packing 750.Y (specific surface area a=750mxe2x88x921, angle of inclination of the passages xcfx86=42.5xc2x0) has 5.5 separation stages per meter (n=5.5). If the angle is increased to 50xc2x0, then the packing surface area which is required for the material separation can be reduced to 500 m2/m3, through which the cost and complexity for the packing material is reduced to 66%. In this the separation performance, at a practically unchanged flow resistance of the packing (pressure loss xcex94p=2 mbar/m at F=vGxcfx81G=1.5 Pa0.5), likewise remains unchanged. Additional material could be saved for the same separation performance, at the price, however, of an increased flow resistance (for a=450 mxe2x88x921 and xcfx86=57xc2x0, xcex94p=2.7 mbar/m).
For the packing 500.Y (a=500 mxe2x88x921, xcfx86=42.5xc2x0), n=4.5. For xcfx86=46xc2x0, a=450 mxe2x88x921, i.e. the material cost and complexity is reduced to 90%, with the flow resistance being practically unchanged. For xcfx86=50xc2x0, a=400 mxe2x88x921, (material cost and complexity 80%), but the flow resistance increases to 123% of the value to be expected for the packing 500.Y.